With recent reductions in the size and thickness of portable telephones and the like, similar reductions in the size and thickness of an image pickup lens unit incorporated into the portable telephone or the like have become necessary. At the same time, however, demand for increased precision therein has increased. As a result, a contradictory problem has arisen in that the lens unit must be reduced in size while making an optical lens as large as possible in order to increase the precision of an optical performance. To solve this problem, it has become important to reduce the size of a holder.
A conventional image pickup lens unit is embedded in the holder so that the optical lens is held peripherally, and in a camera module including this lens unit, an IR cut filter is disposed between the lens and an imaging device. The IR cut filter is typically assembled by a method of fixing the IR cut filter to the holder of the lens unit using an adhesive after the lens unit has been molded. With this method, however, a surface area to which the adhesive is applied decreases as the size of the camera module is reduced, making it difficult to fix the IR cut filter reliably.
To solve the problem of defective adhesion caused by a reduction in the adhesion surface area, a method of forming the IR cut filter by insert-molding so that the IR cut filter can be fixed reliably without using an adhesive has been proposed (see Patent Document 1). In this method, the IR cut filter is set in a housing mold, whereupon resin is introduced such that the IR cut filter is molded integrally with the housing, and simultaneously a peripheral edge portion of the IR cut filter is embedded in the housing. As a result, a fixing surface area of the IR cut filter is secured while achieving a reduction in the size of the holder in comparison with the method of fixing the IR cut filter using an adhesive. However, when the holder portion of the lens unit and the housing of the IR cut filter are molded separately, the number of processes increases, leading to new problems of an increase in cost and a reduction in yield.